[R] S4 non-virtual class with no slots?

[Boylan, Ross]

It seems that if an S4 class has no slots it can't be instantiated because it is assumed to be virtual.  Is there a way around this other than adding a do-nothing slot?  A singleton would be OK, though is not essential.

Problem:
EmptyFitResult <- setClass("EmptyFitResult", representation=representation())
# also tried it without the second argument.  same result.
 > e <- EmptyFitResult()
 Error in new("EmptyFitResult", ...) :
   trying to generate an object from a virtual class ("EmptyFitResult")

This in R 3.1.1.

Context:
I fit simulated data; in some simulations none survive to the second stage of fitting.  So I just need a way to record that this happened, in a way that integrates with my other non-null results.

Thanks.
Ross Boylan